Diaphragm cells have been used for many years for the electrolysis of brines and the formation of chlorine and caustic. These cells have an anolyte chamber separated from a catholyte chamber by a porous diaphragm which has customarily been made of fibrous asbestos that has been deposited upon a porous, metal cathode. Brine is fed into the anolyte chamber, where chlorine is produced, and the anolyte liquor then passes through the asbestos diaphragm into the catholyte chamber. Here caustic is produced and is later recovered from the cell effluent.
The service life of asbestos diaphragms is in the range of six months, as compared to an anode life of 3 to 4 years or more for the new metal anodes. Accordingly, the replacement of cell diaphragms has become now a principal factor in cell outage.
These problems have been attacked by replacement of asbestos with various plastics in the production of cell diaphragms; by reinforcing asbestos fibers with a variety of polymers (e.g. fluorocarbons, U.S. Pat. Nos. 3,944,477 and 3,694,281); and by treating asbestos fibers with inorganic coating agents, such as alkali metal ions (U.S. Pat. No. 3,402,929).